The present invention is directed to an electrode comb or device and a device and method for manufacturing an electrode comb which has at least two rows of wire pieces acting as needle-like recording electrodes which are arranged in a rib of a molded body with the wires of one row being offset by half the distance between the wires of the second row. The method and the device include providing a mold member composed of two halves which are assembled together in one position to form a winding core which has recesses on opposite outer surfaces and on which a wire is wound with the turns being joined to circuit boards disposed in the recesses clamped and severed. Then the two halves are disassembled and reassembled with the recesses facing each other to form a mold cavity into which a resin compound is injected to form the electrode comb. Subsequent to hardening of the resin compound, the exposed ends of the wires are trimmed to be flush with the surface of a recording edge of the molded body.
Electrode combs which have at least one row of needle-like recording electrodes are required for producing exact copies of a master on a copy paper. The combs are utilized to charge point-by-point the copy paper in accordance with the electrode arrangement so that a toner will adhere to the corresponding points when it is applied. In order to obtain a high recording quality of eight points per millimeter, the electrodes are usually disposed in two rows having respective spacing of 250 um and the electrodes in one row are offset by 125 um from the electrodes of the other row. Thus, the electrode comb generally contains up to 2000 recording electrodes, which are disposed parallel to one another and are fixed by means of a thermosetting plastic resin. For the purpose of manufacturing such needle electrodes, a wire is usually wound on a winding core or mold with each turn of the winding having a specific lead or pitch. After the individual windings are fixed with the assistance of the thermosetting resin, the individual windings are again severed.
A device for manufacturing an electrode comb composed of numerous needle-shaped electrodes is disclosed by German LP 22 61 529. A multi-part mold having an upper and lower mold part is utilized. The lower mold part has a planar top surface and an essentially convexly rounded underside. In the upper area or top surface, lateral faces of the lower mold part have planar surface parts against which printed circuit boards are seated. After a wire has been wound around the lower mold part, each of the turns is connected such as by soldering to conductor paths or circuits of each circuit board. The upper surface of the lower mold part has two rectangular recesses which extend parallel to one another and to the longitudinal axis of the part and these recesses receive an injection or casting resin compound. An upper mold part has a surface corresponding to the upper surface of the lower mold part with corresponding recesses. Thus, after a wire has been wound on the lower mold part with the windings having a predetermined, mutual spacing and the wires being secured to the appropriate conductor paths in the circuit boards, the upper mold part is then placed on the upper surface of the lower mold part. Subsequently, the resin compound is injected into the cavities of the two mold parts to form two resin strips with a respective row of recording electrodes therein. After hardening of the resin, the part of the wire winding extending between the two recesses is cut so that two units with each having a resin strip containing a row of needle-shaped electrodes are produced. The two faces of these two parts are joined together to form the electrode comb. The joining of the two strips must be undertaken with the needle electrodes of the two rows being mutually offset so that the needles of the one row are respectively opposite the space between the two needles of the other row and such that the ends of the needles proceed in two straight longitudinal rows from one end to the other end of the part. This presupposes not only a very precise manufacturing of the strips containing the rows of electrodes but a rather precise joining of the two strips a well. Another disadvantage of the comb provided in this manner is that the strips containing the rows of electrodes are connected to each of the printed circuit boards only by the flexible wires of the winding so that there is always the hazard of damaging the individual wires.